Download Builder Insight No. 12 - Reducing Energy Use in Multi

Number
Builder
Insight
12
technical maintenance bulletin
Energy Use in Mid to High-Rise
Multi-Unit Residential Buildings
Mid to high-rise multi-unit residential buildings (MURBs)
consume a significant amount of energy. Understanding how
MURBs use this energy is essential to reducing energy use and
cost to building owners and occupants.
In Vancouver, approximately 32% of residential gas and 50% of residential
electricity is used in mid and high-rise multi-unit buildings. To better
understand energy use in MURBs, energy consumption data from more
than 60 mid to high-rise condominium buildings was collected and studied.
Information in this bulletin is based on the results of a study in buildings
located on the south coast of British Columbia, primarily in Metro
Vancouver and Victoria. While many general conclusions can be drawn
from the results of the study, they do not necessarily apply to all MURBs.
Each building has unique features and location and therefore its energy
use characteristics are also unique.
Builder Insight is a series of bulletins
and companion videos designed to
provide practical information on
new technologies, research results,
good building practices and emerging
technical issues in residential
construction to Licensed Residential
Builders and others in the industry.
This bulletin is produced by the
Homeowner Protection Office (HPO),
a branch of BC Housing, and was
prepared by RDH Building Engineering
in collaboration with Canada Mortgage
and Housing Corporation, BC Hydro,
Fortis BC, and the City of Vancouver.
Overall Energy Use
Of the initial 64 study buildings, detailed energy
consumption data was analyzed for 39 (34 in Metro
Vancouver and five in Victoria). The average energy use
intensity for the MURBs study was 213 kWh/m2/yr,
with a fairly even distribution between 144 to 299 kWh/
m2/yr. On average, 51% of this energy is attributable
to the burning of natural gas (make-up air units,
hot water and gas fireplaces), 28% to electricity used
in individual suites (electric heat, lighting, appliances,
outlets, etc.) and 21% to electricity supplied to common
areas (lighting, elevators, fans, pumps, common space
heating, etc.).
It is interesting to look at the annual energy
consumption on a per suite basis. Buildings with
larger suites can have a higher total energy
consumption that is not as apparent when looking
at it on a per floor area basis. Although building 57
is within the middle group by floor area, it has the
highest energy consumption by far when looking at
it on a per suite basis. Its high energy consumption
is attributed to the fact that this building is a high-end
condominium with suites in the 2000+ ft2 range with
full amenities, including air conditioning, in-suite
fireplaces, and common area recreation centre and pool.
Total normalized energy consumption by floor area.
Total energy consumption normalized by suite.
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in locations that would maximize space heating
potential.
The figure below shows how energy is typically
consumed in a MURB. Building simulations were used
to determine the typical contribution of space heating
energy of fireplaces. When no fireplace is present,
in-suite electrical space heating energy consumption
is approximately 16% higher. However, total in-suite
space heating energy, including electricity and
natural gas, can more than double with the presence
of a fireplace as shown in the bar chart below.
Decorative fireplaces are generally installed in MURBs
and are placed in locations that tend to enhance
aesthetic value. The performance of fireplaces could be
improved with more efficient fireplaces installed
Distribution of annual energy consumption
in a typical MURB. Units shown in kWh/m2/yr
and as percentage of total consumption.
Newer buildings (built after about 1990) typically
used more energy than older buildings (built in the
1970s and 80s). This is due, in part, to increased
ventilation requirements for new buildings that
result in more outdoor air that is heated as it is
brought into the building. Additionally, newer
buildings typically had more amenities such as pools,
saunas and exercise rooms. Gas fireplaces that were
relatively inefficient at space heating were also found
to be more common in newer buildings.
The overall thermal performance of newer MURBs
appears to have decreased slightly relative to older
MURBs, and the heat loss through the building
enclosure remains significant. Several newer buildings
in the study had overall effective enclosure R-values in
the range of R-2.0 hr∙ft2•°F/Btu, due to higher glazing
percentages (window to wall ratio) and large thermal
bridges (exposed slab edges, balconies, steel framing
etc.). The study found that buildings constructed before
the year 2000 had average pre rehabilitation R-values
of R-2.5 effective.
Comparison of annual space heat
consumption for buildings with and
without fireplaces.
b u i l d e r i n s i g h t No . 12
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energy costs
The average energy cost per suite was roughly
$1,200 ($1.10/sq ft) per year, 39% of which is paid by
the owner or occupant, and 61% is paid by the strata
corporation. These costs assume 2013 utility rates of
8¢/kwh for electricity and $9/GJ for natural gas. In
buildings with fireplaces, an average of $160/year is
added to the per suite total natural gas costs paid
by the strata.
Paid by Strata Corporation
Paid by Suite Owner or Occupant
Natural Gas,
$380, 31%
Suite
Electricity,
$470, 39%
energy use trends
Make-up air units (Maus)
• The gas used to heat ventilation air by MAUs is often
the largest single component of energy use within
MURBs, particularly those constructed in the past
decade, which have higher design ventilation rates.
while space heating in most buildings is intended to
be primarily provided by electric baseboard heaters,
in many cases a large portion of the space heating
energy in the building is provided within the ventilation air heated by the MAU. On average, 69% of the
total space heating energy is consumed by the MAU.
• Typically, the set point temperature for air delivered
to the building from the MAU is set higher than
20°C (68°f). Corridor temperatures do not need to
be maintained that warm. A temperature of 16°C to
18°C (60°f to 64°F) would significantly reduce energy
consumption. Building simulations performed for
the study found that reducing the temperature from
20°C to 16°C (68°f to 60°f) can reduce MAU gas
consumption by approximately 21%. The lower air
temperature would, in turn, increase in-suite
electrical heating energy by around 15%, for a total
building space heating savings of roughly 12%.
• while ventilation air is intended to be delivered to
suites by the MAU through the pressurized
corridor, much of the air this unit provides is lost
to the outdoors through stairwells, elevator shafts,
etc., before it reaches the suites. Door threshold
sweeps are often installed by occupants to reduce
noise, odours, or light from the corridors, but they
also block the entry of make-up air. further, the MAU
system is a supply only system which means that no
provisions are put in place for continuous exhaust of
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HOMEOwn ER PROTECTIOn OffIC E
Common
Electricity,
$370, 30%
stale air from the suites to allow air from the MAU
to readily enter the suite.
In new MURB construction and major building
rehabilitation projects, moving away from the
traditional pressurized corridor approach to a
compartmentalized suite approach where each suite
has its own heating and ventilation system would
have many benefits:
• The amount of outdoor air to the suites would be
better regulated.
• The suite owners could be billed for their individual
space heating and ventilation needs.
• Preheated outdoor air lost through the building
would be reduced.
• It would allow for the implementation of heat
recovery ventilators (HRV). By recovering heat from
the exhaust air before it is exhausted outside,
average space heating savings of approximately
34% could be achieved with an 80% efficient
in-suite HRV.
Electric Baseboard Heating
• For the 39 study buildings, on average 69% of
the purchased energy for space heating is for gas
(through the MAU, ventilation system), with a range
from 40% to 97%. The remaining 31% of the space
heating is used by electric baseboard heaters (the
primary heating system) with a range from 3% to
60%. This electrical space heating accounts for 38%
of the suite electricity consumption (range of
6% to 61%). It is also typical for some owners to
purchase small electric space heaters to supplement
baseboard heaters, particularly for unheated rooms
such as enclosed balconies.
Natural Gas Fireplaces
•While electric baseboard heaters are usually the
intended primary source of space heating, fireplaces
are frequently used to provide space heating. Not
only do some occupants prefer to use fireplaces for
personal preference and aesthetics, there is also an
incentive to heat with fireplaces as the utility bill
is paid by the strata corporation as opposed to
electrical space heating that is paid directly by the
suite owners. However, in the end, suite owners pay
more as their monthly condo fees are increased by
an amount higher than their electricity savings.
• Traditional decorative gas fireplaces are inefficient
at space heating and can consume approximately
18% of the energy in a MURB. Pilot lights can
consume up to 50% of the fireplace energy
consumption. Strata or owner groups may wish to
consider building-wide pilot light shut-off for the
summer months. Turning the pilot lights off for
six months of the year can reduce fireplace gas
consumption by up to 25%. It can also reduce cooling
costs, where cooling is present, and improve thermal
comfort during the summer. It is also a good idea
to install fireplace timers as these are relatively
inexpensive and easy to install and are good at
reducing gas consumption.
Domestic Hot Water
• With the exception of one study building that had
in-suite electric Domestic Hot Water (DHW) tanks,
DHW was provided to units from a central natural gas
boiler. There was a big range of DHW energy
consumption values from one building to another
going from a low of 14 kWh/m2/yr and 9% of the
building energy consumption, to a high of 77 kWh/
m2/yr and 35% of building energy consumption. There
was only a slight correlation in total building DHW
consumption and the number of suites in the building,
with much of the energy use being inconsistent.
Elevators
• A number of MURBs constructed in the 1980s-1990s
had AC-DC elevator motor convertors that were
running continuously (timers broken or not installed),
resulting in a significant amount of wasted energy.
Lighting
• Lighting energy consumption on average consumed
10% of the building energy use, of which 20% was
for common area lighting/parking garages and
80% for in-suite lighting. There are opportunities
to save energy in common areas through the use
of occupancy and/or daylight sensors, as they are
typically on 24 hours a day, seven days a week. Lights
and fixtures can also be replaced with compact
fluorescents and more energy efficient fluorescent
light bulbs and ballasts at a relatively low cost and
acceptable payback. Lighting upgrades within suites
are also possible (i.e. to CFLs or LEDs), yet these are
generally upgraded by the suite occupants.
b u i l d e r i n s i g h t No . 12
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Building Enclosure Air Leakage
• There is limited data on overall MURB airtightness
as it is more complex to measure building enclosure
air leakage of a MURB compared to a house. The
use of operable windows (particularly in temperate
climates) further invalidates most estimates of
operating building pressures, building enclosure
airtightness, and suite ventilation/heating
distribution. Simulations were completed to
determine the impact of the airtightness of the
building enclosure on energy consumption.
The baseline simulations assumed an average
airtightness of 0.15 cfm/ft2 at normal operating
pressures. A series of air leakage rates were
simulated, ranging from very tight to average to
very leaky, to determine the energy impact of
varying the air leakage rate. Reducing the air leakage
rate to 0.02 cfm/ft2 decreased energy use by 8.5%,
whereas increasing the rate to 0.4 cfm/ft2 increased
consumption by 8.6%. When increasing the
airtightess of a building, it is important to ensure
that there is adequate outdoor air provided to all
of the suites.
Building Enclosure Rehabilitation and
Renewals Projects
Many multi-unit residential buildings in British
Columbia and other parts of North America have or
are undergoing comprehensive building enclosure
rehabilitation, largely to remedy moisture-related
problems. In other instances, buildings need to
undergo renewals of building enclosure assemblies as
part of the facility upkeep. Unfortunately, for reasons
primarily related to short-term costs, little or no
attention is typically directed at energy conservation
when implementing these projects. The study found
that even without energy efficiency in mind, important
energy savings are being realized by improved enclosure
assemblies and details (e.g. energy efficient windows,
reduced thermal bridging and improved airtighness).
Even more significant savings could be achieved if
energy efficiency was given more consideration.
Summary of calculated overall effective enclosure R-values
(pre and post rehabilitation).
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Energy use was analyzed in 13 study buildings that
underwent a full (walls, windows, roof) building
enclosure rehabilitation to address moisture damage.
As part of this analysis, detailed enclosure thermal
performance characteristics were determined.
The overall R-value of rehabilitated buildings
improved from an average of R-2.4 hr∙ft2·°F/Btu
(pre rehabilitation) to R-3.4 (post rehabilitation), even
though the rehabilitation work focused on the correction
of water ingress problems, and not to improve the
heat transfer characteristics of these buildings.
Average energy consumption for the 13 buildings
analyzed in greater detail was 203 kWh/m2/year
pre rehabilitation and 188 kWh/m2/year post
rehabilitation. On average, the building enclosure
rehabilitations resulted in space-heat energy savings
in the order of 14% and total energy savings of
approximately 8%. This was substantial given that
energy efficiency was not a primary design concern
for the rehabilitations. Energy use was reduced
during these rehabilitations primarily because of the
improved thermal efficiency (exterior insulation and
reduced thermal bridging effects) and improved
airtightness (full exterior air barrier and more airtight
windows/doors).
Recommendations for the MURB
Construction Industry
A number of recommendations were developed based
on the results of the study. These recommendations
can be used to guide changes in new building design
and construction practices. They also present
opportunities to improve the performance of existing
building stock:
• Reduce the heating and cooling loads by improving
the thermal performance of the building enclosure.
Design new buildings and retrofits with more
insulation, better windows, lower window to wall
area ratios, enclosures with less thermal bridging
and therefore improved overall effective R-values.
suites minimizing air leakage and making it easier
to install heat recovery ventilators to recover heat
from the exhaust air.
• Engage and educate building developers, owners
and occupants to enhance understanding of where
and how energy is used within their building.
• Address the disconnect between energy use and
payment for consumption through individual suite
energy metering.
Energy Saving Opportunities for Owners
and Managers
A wide range of measures exist to help save energy in
MURBs that vary significantly in scale and cost. Some
smaller scale strategies to reduce energy consumption
include:
• Tune-up existing systems including the make-up air
units.
• Lower the make-up air temperature set-point and
adjust flow rates to required levels.
• Reduce the use of gas fireplaces as a source of heat
and implement building-wide shut-off of pilot lights
for half the year when fireplaces are not in use.
• Educate building occupants about their building’s
energy consumption.
Larger projects, such as improving the insulation levels
of a building or installing more thermally efficient
windows, may prove too expensive for many owner
groups when simple payback periods alone are
considered. However, when energy conservation
measures are integrated with building maintenance
and renewals activities, significant cost effective
opportunities exist to reduce consumption.
• Control airflow within MURBs through airtight
enclosures, compartmentalization of floors and
suites, and more efficient ventilation systems.
Enable outdoor air to be provided directly to the
b u i l d e r i n s i g h t No . 12
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Key Points
• Energy consumption was analyzed in 39 Lower
Mainland mid to high-rise MURBs.
• Average energy consumption is roughly half natural
gas and half electricity.
• The most energy is used to heat outdoor air for
ventilation. Significant savings can be achieved by
simply lowering the temperature set-point used in
the make-up air unit.
• Significant savings can be achieved by simply
turning off fireplace pilot lights during summer
months throughout the building.
• In general, energy consumption was not found to
be lower in newer buildings due to a variety of
combined factors.
• Roughly two-thirds of the energy is paid indirectly
by suite owners through strata fees.
• Great opportunities exist to reduce energy
consumption during building rehabilitations and
renewals, with study buildings that were fully
retrofitted achieving 14% space heating savings even
though energy efficiency was not a primary design
consideration.
Mid to high-rise multi-unit
buildings (MURBs) consume a
significant amount of energy.
For More Information
1. Subscribe to receive Builder Insight bulletins
published by the Homeowner Protection Office
(HPO) and available online at www.hpo.bc.ca
2.Energy Consumption and Conservation in Mid and
High Rise Residential Buildings in British Columbia,
Research Report available at www.hpo.bc.ca
3.Maintenance Matters bulletins available online at
www.hpo.bc.ca. Specifically, the bulletins entitled
Reducing Energy Use in Multi-Unit Residential
Building, and Building Envelope Maintenance and
Renewals Planning
4.About Your Apartment: Energy and Water-Saving Tips
for Your Apartment, CMHC Publication available at
www.cmhc-schl.gc.ca
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HPO Technical Research
& Education
1701- 4555 Kingsway
Burnaby, BC V5H 4V8
Phone: 778 452 6454
Toll-free: 1 866 465 6873
www.hpo.bc.ca
www.bchousing.org
Email: [email protected]
10/13
The greatest care has been taken to confirm the accuracy
of the information contained herein. However, the authors,
funder and publisher assume no liability for any damage,
injury or expense that may be incurred or suffered as a result
of the use of this publication including products, building
techniques or practices. The views expressed herein do not
necessarily represent those of any individual contributor
or BC Housing. It is always advisable to seek specific
information on the use of products in any application or
detail from manufacturers or suppliers of the products and
consultants with appropriate qualifications and experience.
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